The National Library of Finland The National Library of Finland TR-Sys The International Standard Book Number, ISBN, is a widely used identifier for monographic publications. Since 2001, the URN (Uniform Resource Name) namespace "ISBN" has been reserved for ISBNs. The namespace registration was performed in RFC 3187 and applied only to the ISBN as specified in the ISO Standard 2108-1992, now known as "ISBN-10". To allow for further growth in use, the successor ISO Standard, ISO 2108:2005, has defined an expanded format for the ISBN, known as "ISBN-13". This document defines how both of these ISBN standard versions can be supported within the URN framework. Moreover, additional query and fragment usage related information required by RFC 2141bis has been included. An updated namespace registration conformant to RFC 3406bis is provided. It describes how both the old and the new ISBN format can share the same namespace. This document replaces RFC 3187; it also obsoletes and moves to Historic status the predecessor thereof, RFC 2288.